Liquid crystal display device

ABSTRACT

The liquid crystal display device includes: a substantially rectangular optical switching member in which a first polarizer, a first substrate, a second substrate, and a second polarizer are sequentially provided from a front surface side; a frame which surrounds the optical switching member; a planar light source which is disposed at the rear surface of the optical switching member; at least one optical sheet group which is disposed at the front surface of the planar light source; and an adhesive layer which fixes the optical switching member, the frame, and the optical sheet group to each other, and has a substantially rectangular opening, wherein at least one side of an optical sheet included in the optical sheet group and located at the frontmost surface is adhered to the adhesive layer, and the other sides are located inside the opening of the adhesive layer.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese application JP2010-034110 filed on Feb. 18, 2010, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device.

2. Description of the Related Art

There has been an increasing demand for a decrease in thickness of asmall and medium-sized liquid crystal display device used in a portabledevice, etc. in order to reduce the volume or weight thereof. Here, thesmall and medium-sized liquid crystal display device has a typicalstructure in which two polarizers and two glass substrates constitutingan optical switching member, and a light guiding plate constituting aplanar light source, and plural optical sheets disposed therebetween arestacked, and the stacked structure is fixed to a frame by an adhesivesheet.

JP 2007-163556 A discloses a structure that decreases the thickness ofthe liquid crystal display device, where an external shape of apolarizer at the rear surface side is set to be smaller than an openinginside an adhesive sheet so that the polarizer is accommodated therein,and a frame and a glass substrate (generally, called a TFT substrate) atthe rear surface side are directly fixed to each other by the adhesivesheet.

In the small and medium-sized liquid crystal display device, not only adecrease in thickness described above, but also a decrease in framearea, that is, a decrease in width between an end portion of an areadisplaying an image and an end portion of the liquid crystal displaydevice have been demanded.

In the liquid crystal display device disclosed in JP 2007-163556 A, thewidth of the adhesive sheet used to fix the frame and the rear surfaceside glass substrate to each other needs to be narrowed in order toreduce the frame area. However, there is a limit in processing in orderto form the adhesive sheet to have a narrow width, and to accuratelyadhere the adhesive sheet to a corresponding member.

SUMMARY OF THE INVENTION

The invention is made in view of such circumstances, and aides a liquidcrystal display device that is thin as a whole and has a narrow framearea.

Of aspects of the present invention disclosed by this application, abrief outline of representative aspects is described as follows.

(1) A liquid crystal display device includes: a substantiallyrectangular optical switching member in which a first polarizer, a firstsubstrate, a second substrate, and a second polarizer are sequentiallyprovided from a front surface side; a frame which surrounds the opticalswitching member; a planar light source which is disposed on the rearsurface side of the optical switching member; at least one optical sheetgroup which is disposed at the front surface of the planar light source;and an adhesive layer which fixes the optical switching member, theframe, and the planar light source to each other, and has asubstantially rectangular opening, wherein at least one side of anoptical sheet included in the optical sheet group and located at thefrontmost surface is adhered to the adhesive layer, and the other sidesare located inside the opening of the adhesive layer.

(2) In the liquid crystal display device of (1), the optical sheet groupincludes at least one first optical sheet group having an optical sheetlocated at the frontmost surface and at least one second optical sheetgroup having an optical sheet located at the rearmost surface; and theother side of the optical sheet included in the second optical sheetgroup and located at the frontmost surface is adhered to the adhesivelayer.

(3) In the liquid crystal display device of (2), the first optical sheetgroup includes a first tongue-shaped portion that protrudes from a partof the one side thereof; and the first tongue-shaped portion of theoptical sheet included in the first optical sheet group and located atthe frontmost surface is adhered to the adhesive layer.

(4) In the liquid crystal display device of (3), the second opticalsheet group includes a second tongue-shaped portion that protrudes froma portion except for the first tongue-shaped portion of the one side;and the second tongue-shaped portion of the optical sheet included inthe second optical sheet group and located at the frontmost surface isadhered to the adhesive layer.

(5) In the liquid crystal display device of any of (1) to (4), the framehas a step structure on the inside of the one side, and the opticalsheet located at the frontmost surface is interposed between theadhesive layer and the step structure.

According to the invention disclosed in the application, the liquidcrystal display device may be provided that is thin as a whole and has anarrow frame area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view illustrating a liquid crystaldisplay device according to a first embodiment.

FIG. 2 is a plan view illustrating the liquid crystal display deviceaccording to the first embodiment.

FIG. 3 is a cross-sectional view taken along the line A-A of FIG. 2.

FIG. 4 is a cross-sectional view taken along the line B-B of FIG. 2.

FIG. 5 is a cross-sectional view taken along the line C-C of FIG. 2.

FIG. 6 is an exploded perspective view illustrating a liquid crystaldisplay device according to a second embodiment.

FIG. 7 is a plan view illustrating the liquid crystal display deviceaccording to the second embodiment.

FIG. 8 is a cross-sectional view taken along the line D-D of FIG. 7.

FIG. 9 is a cross-sectional view taken along the line E-E of FIG. 7.

FIG. 10 is an exploded perspective view illustrating a liquid crystaldisplay device according to a third embodiment.

FIG. 11 is a cross-sectional view taken along the line B-B of FIG. 2 ofthe third embodiment.

FIG. 12 is a cross-sectional view taken along the line C-C of FIG. 2 ofthe third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a first embodiment of the invention will be described byreferring to the drawings.

FIG. 1 is an exploded perspective view illustrating a liquid crystaldisplay device 100 according to the first embodiment of the invention.The liquid crystal display device 100 includes an optical switchingmember 1, an adhesive sheet 2 which is an adhesive layer, a frame 3, aplanar light source 4, and an optical sheet group 5. Further, a user maysee an image displayed on the liquid crystal display device 100 from theupside of the same drawing. Hereinafter, the up direction of the samedrawing will be referred to as the front surface side, the oppositedirection thereof will be referred to as the rear surface side, thesurface facing the front surface side will be referred to as the frontsurface, and the surface facing the opposite side thereof will bereferred to as the rear surface.

An optical switching member 1 has a structure in which a first polarizer11, a first substrate 12, a second substrate 13, and a second polarizer14 are sequentially laminated in this order from the front surface side,and has a substantially rectangular shape when taken as a whole. Thefirst substrate 12 is generally called a color filter substrate in whichred, blue, and green films are provided for each pixel when the liquidcrystal display device 100 is able to display full color. The secondsubstrate 13 is generally called a TFT substrate having thereon pluralelectrodes respectively corresponding to pixels and plural switchingelements such as TFTs (Thin Film Transistors) that control a voltageapplied to the electrodes. A layer formed of liquid crystal is heldbetween the first substrate 12 and the second substrate 13. When avoltage is applied to the electrodes formed on the second substrate 13,the alignment direction of liquid crystal corresponding to each pixelchanges, and a polarization direction of light transmitted through theliquid crystal layer changes in accordance with the change of thealignment direction. The second polarizer 14 and the first polarizer 11are disposed so that transmissivity of light changes in accordance withthe polarization direction of light transmitted through the liquidcrystal layer. Accordingly, the optical switching member 1 serves as amember that changes transmissivity of light for each pixel. Further, thematerials of the first substrate 12 and the second substrate 13 are notparticularly limited as long as they are transparent, but glass is usedin the embodiment. A method of driving liquid crystals may bearbitrarily selected from the generally known methods, and in theembodiment, a method called in-plane switching (IPS) that rotates liquidcrystals within a plane parallel to the substrate is used. However,other methods, for example, vertical alignment (VA) or twisted nematic(TN) may be used.

Further, one side of the second substrate 13 extends so that anextension portion 15 is formed to be longer than the first substrate 12,and the front surface of the extension portion 15 is provided with adriving circuit 16 that drives the switching elements on the secondsubstrate. Interconnection such as a flexible print circuit (FPC) 17 isconnected onto the extension portion 15 so as to connect the liquidcrystal display device 100 to an external device. In the embodiment, thedriving circuit 16 is described as a chip IC mounted on the extensionportion 15, but the driving circuit may be directly formed on the secondsubstrate 13 by a so-called system on glass (SOG).

A spacer 18 is a member that has the substantially same thickness asthat of the second polarizer 14, and is attached to the rear surface ofthe extension portion 15 after mounting the driving circuit 16 on theextension portion. This is because the second polarizer is not disposedat the rear surface of the extension portion 15 in order to prevent thesecond polarizer 14 from being deformed or spoiled when thermallypressing the driving circuit 16 or the FPC 17. Accordingly, the spaceris used to absorb a step generated due to the absence of the secondpolarizer.

As shown in the drawing, the adhesive sheet 2 has a rectangular externalshape with a rectangular opening 21, and in the optical switching member1, three sides except for the side of the extension portion 15 is formedto have a narrow width. The adhesive sheet 2 is an adhesive sheet ofwhich both surfaces are formed as adhesive surfaces, and is used to fixthe optical switching member 1, the frame 3, and the optical sheet group5 to each other. Since the adhesive sheet 2 blocks extra light, theadhesive sheet is preferably black, but may be white or other colors.

The frame 3 is a member that holds the optical switching member 1, theplanar light source 4, and the optical sheet group 5, and supports themas an integrated module, and is preferably formed by plastic injection.However, the material or the manufacturing method of the frame 3 is notparticularly limited.

The external shape of the frame 3 is substantially rectangular, and theframe has a substantially rectangular opening 31 formed therein.Further, in the optical switching member 1, three sides except for theside of the extension portion 15 are provided with ribs 32 along theoutside thereof. The ribs 32 are effectively used to improve therigidity of the frame 3, and to easily help the positioning operation ofthe optical switching member when the optical switching member isdisposed on the frame, but if not necessary, the ribs may not benecessarily provided. The installation position and the length of therib 32 may be arbitrarily set. The opening 31 accommodates the planarlight source 4 and the optical sheet group 5. The inner edge of theopening 31 on the side of the extension portion 15 is provided with astep structure 34 and a concave portion 33 accommodating a lightemitting diode (LED) 41 to be described later. The step structure 34will be described later in detail.

The planar light source 4 includes plural (here, three) LEDs 41, a lightguiding plate 42, and a reflection sheet 43. The LEDs 41 are disposed sothat the light emitting direction faces the side surface of the adjacentlight guiding plate 42. The light guiding plate 42 is formed of atransmissive material, and preferably, transparent plastic, and has anappropriate surface structure such as a groove reflecting light andformed at the rear surface thereof. Light entering from the side surfaceof the light guiding plate 42 facing the LED 41 is guided into the lightguiding plate 42, and is reflected by the surface structure so that thelight is substantially uniformly emitted from the front surface of thelight guiding plate. The reflection sheet 43 reflects the light emittedfrom the rear surface of the light guiding plate 42 so that the lightreturns to the light guiding plate 42. The LEDs 41 are mounted on theFPC 44, and are electrically connected to the extension portion 15 ofthe optical switching member 1 in the embodiment. However, the FPC 44may be connected to an external device without being connected to theoptical switching member 1. Further, the number of the LEDs 41 is notparticularly limited.

The optical sheet group 5 includes plural optical sheets, and is dividedinto a first optical sheet group 51 and a second optical sheet group 52.Further, in the specification, the term of “the optical sheet group” isused as a term generally representing one or more optical sheets.Therefore, plural optical sheets may not be included in “the opticalsheet group”, and only single optical sheet may be included therein.

In the embodiment, the first optical sheet group 51 includes only aprism sheet 53. The second optical sheet group 52 includes a prism sheet54 and a diffusion film 55. The first optical sheet group 51 is disposedon the front surface side in relation to the second optical sheet group52. Further, the shapes of the first optical sheet group 51 and thesecond optical sheet group 52 are slightly different from each other.Specifically, on the side of the extension portion 15 in the opticalswitching member 1, the first optical sheet group 51 is longer than thesecond optical sheet group 52 and extends toward the extension portion15, and on the side of the other sides of the switching member, thefirst optical sheet group 51 is slightly smaller than the second opticalsheet group 52. The dimensions of the optical sheet groups will bedescribed later in detail.

Further, in the embodiment, the optical sheet group 5 includes threeoptical sheets, but the invention is not limited thereto. For example,the optical sheet group 5 may include four or more optical sheets byadding a luminance improving film or other optical compensating films,or may include two optical sheets by omitting any one of the prism sheet53 and the prism sheet 54. In this case, the front surface of the lightguiding plate 42 may be provided with an appropriate surface structurethat serves as the prism sheet. Alternatively, in some cases, only oneoptical sheet may be used. In this case, the optical sheet group 5includes the first optical sheet group 51 only having a single opticalsheet, and does not include the second optical sheet group 52.

FIG. 2 is a plan view illustrating the liquid crystal display device 100according to the embodiment. In the drawing, the above-described membersare shown with their reference numerals given thereto.

FIG. 3 is a cross-sectional view taken along the line A-A of FIG. 2. Asshown in the same drawing, the second polarizer 14 of the opticalswitching member 1 is fixed to the front surface of the frame 3 by theadhesive sheet 2. At the same time, the light guiding plate 42 and theoptical sheet group 5 are accommodated inside the opening 31 of theframe 3, and in the second optical sheet group 52 disposed at the frontsurface of the light guiding plate 42, the prism sheet 54 serving as anoptical sheet and disposed at the frontmost surface is fixed by theadhesive sheet 2. On the other hand, in the optical sheet group 5, theprism sheet 53 of the first optical sheet group 51 as the optical sheetlocated at the frontmost surface is formed to have a dimension that theend portion of the prism sheet is disposed on the inside of the secondoptical sheet group 52, so that the prism sheet is located inside theopening 21 of the adhesive sheet 2. For this reason, the position of theprism sheet 53 in the height direction of the cross-section overlapswith the adhesive sheet 2. Further, in the embodiment, the first opticalsheet group 51 includes only the prism sheet 53, but when the firstoptical sheet group 51 includes plural optical sheets, the dimensions ofthe optical sheets may be the same. The dimension of the second opticalsheet group is substantially the same as that of the light guiding plate42 in the cross-section, but a slight difference in dimension isallowed. The reflection sheet 43 is fixed to the rear surface of theframe 3.

With the above-described configuration, since the adhesive sheet 2simultaneously fixes both the frame 3 and the second optical sheet group52 to the optical switching member 1, the width of the adhesive sheet 2is wide compared with the case where any one of them is fixed.Therefore, the width of the portion indicated by d in the drawing andfixing the frame 3 and the optical switching member 1 may be narrowerthan the process limit of the adhesive sheet 2. Further, since the firstoptical sheet group 51 and the adhesive sheet 2 are disposed at aposition where they overlap with each other in the height direction ofthe cross-section, the respective members constituting the liquidcrystal display device 100 are stacked without any waste in space, sothat the entire thickness thereof is thin.

Further, as shown in the drawing, the dimension and the precision ofeach member may be determined so that a gap demanded for processingerrors is provided between the inner surface of the opening 31 of theframe 3 and the light guiding plate 42, between the prism sheet 53 as anoptical sheet located at the frontmost surface in the first opticalsheet group 51 and the second polarizer 14, and between the opticalswitching member 1 and the rib 32 of the frame 3.

The structure described herein is the cross-section of the left sidesurface in FIG. 2, but the upper side surface and the right side surfacein the same drawing have the same structure.

FIG. 4 is a cross-sectional view taken along the line B-B of FIG. 2.FIG. 4 illustrates the cross-section including the concave portion 33 ofthe frame 3 shown in FIG. 1. Each LED 41 mounted on the FPC 44 isdisposed at each concave portion 33 so that its optical axis faces theright direction in the drawing, and the FPC 44 is fixed to the rearsurface of the frame 3. In the cross-section of the optical switchingmember 1, the second polarizer 14 and the spacer 18 are attached to theadhesive sheet 2 and are fixed onto the frame 3. However, the inventionis not limited thereto, and only the spacer 18 may be adhered to theadhesive sheet 2. Further, the driving circuit 16 and FPC 17 are shownon the front surface of the extension portion 15.

The adhesive sheet 2 extends from the front surface of the frame 3 so asto cover the front surface side of the LED 41. Then, the prism sheet 53as an optical sheet located at the frontmost surface in the firstoptical sheet group 51 extends to the front surface side of the LED 41,and is adhered to the rear surface of the adhesive sheet 2. At thistime, as shown in the drawing, the prism sheet 53 is slightly benttoward the rear surface and is adhered to the rear surface of theadhesive sheet 2. Further, the dimension of the second optical sheetgroup 52 is set so that its end portion is disposed on the inside of thelight guiding plate 42, and hence the prism sheet 53 is not interferedwith by other optical sheets. The position of the end portion of thesecond optical sheet group 52 may be arbitrarily set as long as the endportion is not interfered with by the first optical sheet group 51, andthe invention is not limited to the position where the end portion isdisposed on the inside of the light guiding plate 42 as in theembodiment.

FIG. 5 is a cross-sectional view taken along the line C-C of FIG. 2.FIG. 5 illustrates the cross-section including the step structure 34 ofthe frame 3 shown in FIG. 1. The step structure 34 is disposed at thefront surface of the opening 31 of the frame 3 facing the light guidingplate 42, and the height of the step is set to be substantially equal tothe total thickness of the first optical sheet group 51. In theembodiment, the height of the step is substantially equal to thethickness of the prism sheet 53. In this manner, the first optical sheetgroup 51 is interposed between the adhesive sheet 2 and the stepstructure 34, and is firmly fixed thereto as shown in the same drawing.Therefore, the position of the first optical sheet group 51 is difficultto be deviated.

Further, the step structure 34 is not essentially needed when the firstoptical sheet group 51 and the frame 3 are not interfered with by eachother. Further, the height of the step structure 34 may be larger thanthe total thickness of the first optical sheet group 51.

Subsequently, a second embodiment of the invention will be described byreferring to the drawings. FIG. 6 is an exploded perspective viewillustrating a liquid crystal display device 200 according to the secondembodiment. The embodiment is equal to the first embodiment except thata first optical sheet group 251 and a second optical sheet group 252have different shapes on the side of the extension portion 15.Therefore, the same reference numerals will be given to the samecomponents as those of the first embodiment, and the description thereofwill not be repeated.

As obviously understood from FIG. 6, a prism sheet 253 constituting thefirst optical sheet group 251 includes a first tongue-shaped portion 256that protrudes from a part of the side thereof on the side of theextension portion 15. On the other hand, a prism sheet 254 and adiffusion film 255 constituting the second optical sheet group 252include second tongue-shaped portions 257 that protrude from the portionexcept for the first tongue-shaped portion 256 on the side of theextension portion 15. In other words, the first tongue-shaped portion256 and the second tongue-shaped portions 257 are not formed atpositions where the tongue-shaped portions overlap with each other in aplan view. Preferably, the first tongue-shaped portion 256 and thesecond tongue-shaped portions 257 may be respectively formed incomplementary shapes, that is, may be formed alternately. Further, atthe side of the first optical sheet group 251 on the side of theextension portion 15, the position of the end portion of the portionexcept for the first tongue-shaped portion 256 is disposed on the insideof the end portions of the second tongue-shaped portions 257 of thesecond optical sheet group 252. At the side of the second optical sheetgroup 252 on the side of the extension portion 15, it is preferable thatthe position of the end portion except for the second tongue-shapedportions 257 is disposed slightly on the inside of the end portion ofthe light guiding plate 42.

FIG. 7 is a plan view illustrating the liquid crystal display device 200according to the embodiment. The liquid crystal display device 200 hasthe completely same external shape as that of the liquid crystal displaydevice 100 according to the first embodiment.

The cross-section taken along the line A-A of FIG. 7 is completely thesame as the cross-section of the first embodiment shown in FIG. 3, andthe cross-sections respectively taken along the lines B-B and C-C andincluding the first tongue-shaped portion 256 are completely the same asthose of the first embodiment shown in FIGS. 4 and 5. Therefore, sincethe description for the cross-section is the same as that of the firstembodiment, the repetitive description is not made herein.

FIG. 8 is a cross-sectional view taken along the line D-D of FIG. 7.FIG. 8 illustrates the cross-section including the second tongue-shapedportions 257 shown in FIG. 6 and the concave portion 33 of the frame 3shown in FIG. 6. In the second tongue-shaped portions 257, the prismsheet 254 as an optical sheet located at the frontmost surface in thesecond optical sheet group 252 is adhered to the adhesive sheet 2. Theposition of the end portion of the first optical sheet group 251 isdisposed on the inside of the opening 21 of the adhesive sheet 2.

Further, FIG. 9 is a cross-sectional view taken along the line E-E ofFIG. 7. FIG. 9 illustrates the cross-section including the secondtongue-shaped portions 257 shown in FIG. 6 and the step structure 34 ofthe frame 3 shown in FIG. 6. Even in the cross-section, in the secondtongue-shaped portions 257, the prism sheet 254 as an optical sheetlocated at the frontmost surface in the second optical sheet group 252is adhered to the adhesive sheet 2, and the position of the end portionof the first optical sheet group 251 is disposed on the inside of theopening 21 of the adhesive sheet 2.

In this manner, the second optical sheet group 252 is interposed betweenthe adhesive sheet 2 and the light guiding plate 42, and is firmly fixedthereto. Therefore, the position of the second optical sheet group 252is difficult to be deviated.

In the example of the embodiment, one first tongue-shaped portion 256 isprovided at the center of the side of the first optical sheet group 251on the side of the extension portion 15, but the invention is notlimited thereto. The first tongue-shaped portion 256 may be provided atthe left or right side, and the number thereof may be plural. The sameapplies to the second tongue-shaped portions 257.

Further, a third embodiment of the invention will be described byreferring to the drawings. FIG. 10 is an exploded perspective viewillustrating the liquid crystal display device 300 according to thethird embodiment of the invention. The embodiment is equal to the firstembodiment except that the concave portion is not formed in the frame 3,and a first optical sheet group 351 is formed in a shape furtherextending toward the extension portion 15. Therefore, the same referencenumerals will be given to the same components as those of the firstembodiment, and the description thereof will not be repeated.

Since the plan view of the liquid crystal display device 300 accordingto the embodiment is the same as that of the first embodiment, thecross-section thereof will be described by referring to FIG. 2.

FIG. 11 is a cross-sectional view taken along the line B-B of FIG. 2 inthe third embodiment. The first optical sheet group 351 crosses thefront surface side of the LED 41, and extends to a step structure 334 ofthe frame 3 in the direction of the extension portion 15. Then, thefirst optical sheet group is interposed between the adhesive sheet 2 andthe step structure 334 and is fixed thereto.

FIG. 12 is a cross-sectional view taken along the line C-C of FIG. 2 inthe third embodiment. FIG. 12 is equal to FIG. 11 except that the LEDs41 are not shown in the drawing.

As in the liquid crystal display device 300 according to the embodiment,the frame 3 may not be essentially provided with the concave portion.However, when the concave portion 33 is formed as in the firstembodiment, the positioning operation of the LEDs 41 may be easilyperformed during the assembly. Further, the external shape of theexpensive first optical sheet group 51 slightly becomes smaller, and thecost involved with material is reduced.

In the above-described embodiments, a case has been described in whichthe first optical sheet group includes a single optical sheet, and thesecond optical sheet group includes two optical sheets, but the numberof optical sheets for each optical sheet group may be appropriatelydetermined in consideration of the thickness of the optical sheet to beused and the thickness of the adhesive sheet. For example, when thethickness of each optical sheet to be used is 65 μm, and the thicknessof the adhesive sheet is 70 μm, the first optical sheet group mayinclude a single optical sheet. When the thickness of each optical sheetis 50 μm, the first optical sheet group may include a single opticalsheet, and the thin adhesive sheet is used such as to be, for example,55 μm. Alternatively, the first optical sheet group may include twooptical sheets so that the total thickness is 100 μm, and the adhesivesheet having 105 μm of thickness may be used. In any case, the number ofoptical sheets respectively allocated to the first optical sheet groupand the second optical sheet group needs to be determined inconsideration of an error or a thickness of a material to be used sothat the liquid crystal display device is thin as a whole.

Further, in the above-described embodiments, the LEDs are disposed onlyat one side surface of the light guiding plate, but may be disposed atother side surfaces, for example, two facing side surfaces. In thiscase, in the optical sheet group, not only one side of the optical sheetlocated at the frontmost surface, but also two opposite sides thereofmay be fixed to the adhesive sheet. In other words, at least one side ofthe optical sheet located at the frontmost surface may be adhered to theadhesive sheet.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaims coverall such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A liquid crystal display device comprising: asubstantially rectangular optical switching member in which a firstpolarizer, a first substrate, a second substrate, and a second polarizerare sequentially provided from a front surface side; a frame whichsurrounds the optical switching member; a planar light source which isdisposed on the rear surface side of the optical switching member; atleast one optical sheet group which is disposed at the front surface ofthe planar light source; and an adhesive layer which fixes the opticalswitching member, the frame, and the optical sheet group to each other,and has a substantially rectangular opening, wherein a surface at leastone side of an optical sheet included in the optical sheet group andlocated at the frontmost surface of the optical sheet group is adheredto the adhesive layer, and at least one other side of the frontmostsurface of the optical sheet is located inside the opening of theadhesive layer so as not to be adhered to the adhesive layer.
 2. Theliquid crystal display device according to claim 1, wherein the opticalsheet group includes at least one first optical sheet group having theoptical sheet located at the frontmost surface and at least one secondoptical sheet group having an optical sheet located at the rearmostsurface, and wherein a surface at least one side of the optical sheetincluded in the second optical sheet group and located at the frontmostsurface of the second optical sheet group is adhered to the adhesivelayer.
 3. The liquid crystal display device according to claim 2,wherein the first optical sheet group includes a first tongue-shapedportion that protrudes from a part of the one side thereof, and whereinthe first tongue-shaped portion of the optical sheet included in thefirst optical sheet group and located at the frontmost surface isadhered to the adhesive layer.
 4. The liquid crystal display deviceaccording to claim 3, wherein the second optical sheet group includes asecond tongue-shaped portion that protrudes from a portion other thanthe first tongue-shaped portion of the one side of the optical sheet ofthe first optical sheet group, and wherein the second tongue-shapedportion of the optical sheet included in the second optical sheet groupand located at the frontmost surface is adhered to the adhesive layer.5. The liquid crystal display device according to claim 1, wherein theframe has a step structure on the inside of the one side, and theoptical sheet located at the frontmost surface is interposed between theadhesive layer and the step structure.
 6. The liquid crystal displaydevice according to claim 1, wherein the optical sheet of the opticalsheet group is substantially rectangular in shape and the foremostsurface of the optical sheet of the optical sheet group at only one sideof the optical sheet is adhered to the adhesive layer and the foremostsurface at three other sides of the optical sheet are located inside theopening of the adhesive layer so as not to be adhered to the adhesivelayer.